Paper has been used as a medium for recording various types of information for a very long time, and many types of information are even now recorded on paper. On the other hand, with advancements in industries, films for recording image information and record disks for recording sound information have been made available. In recent years, due to wide use of computers, there have been used magnetic recording media, optical recording media, semiconductor recording media and others as media for recording digital data.
The above-described information recording media are provided with durability to such an extent that will not cause any trouble in using them, depending on individual use. It may be safe to say that information recording media, for example, printed matter of paper, film and record disks are media which are sufficiently durable when used on a time scale of several years. However, on a time scale of several decades, these information recording media will inevitably deteriorate with the lapse of time and may be unable to maintain recorded information. Further, they may be damaged not only with the lapse of time but also by water and thermal influences.
Further, magnetic recording media, optical recording media, semiconductor recording media and others for computers are provided with durability to such an extent that will not cause trouble in using general electronic devices. However, these media are not designed, with durability on a time scale of several decades taken into account and, therefore, not suitable as permanent information storage media.
On the other hand, in Patent Document 1 given below, as a method for recording information on a durable medium like quartz glass, with a recording capacity enhanced, there has been disclosed a method in which data is recorded three dimensionally at small cells within a cylindrical medium based on a difference in light transmittance, and while the medium is rotated, computer tomography technology is utilized to read out the information. Further, in Patent Document 2, there has been disclosed a method in which in order to attain the same purpose, a cylindrical recording medium is exposed to irradiation of electromagnetic waves by changing an irradiation angle to measure a difference in transmittance and read out information also by utilizing the computer tomography technology.